The University of Texas, Austin, 78712-1071, United States.
Bioorg Chem. 2010 Dec;38(6):252-9. doi: 10.1016/j.bioorg.2010.07.002. Epub 2010 Jul 18.
The tautomerase superfamily consists of structurally homologous proteins that are characterized by a β-α-β fold and a catalytic amino-terminal proline. 4-Oxalocrotonate tautomerase (4-OT) family members have been identified and categorized into five subfamilies on the basis of multiple sequence alignments and the conservation of key catalytic and structural residues. Representative members from two subfamilies have been cloned, expressed, purified, and subjected to kinetic and structural characterization. The crystal structure of DmpI from Helicobacter pylori (HpDmpI), a 4-OT homolog in subfamily 3, has been determined to high resolution (1.8Å and 2.1Å) in two different space groups. HpDmpI is a homohexamer with an active site cavity that includes Pro-1, but lacks the equivalent of Arg-11 and Arg-39 found in 4-OT. Instead, the side chain of Lys-36 replaces that of Arg-11 in a manner similar to that observed in the trimeric macrophage migration inhibitory factor (MIF), which is the title protein of another family in the superfamily. The electrostatic surface of the active site is also quite different and suggests that HpDmpI might prefer small, monoacid substrates. A kinetic analysis of the enzyme is consistent with the structural analysis, but a biological role for the enzyme remains elusive. The crystal structure of DmpI from Archaeoglobus fulgidus (AfDmpI), a 4-OT homolog in subfamily-4, has been determined to 2.4Å resolution. AfDmpI is also a homohexamer, with a proposed active site cavity that includes Pro-1, but lacks any other residues that are readily identified as catalytic ones related to 4-OT activity. Indeed, the electrostatic potential of the active site differs significantly in that it is mostly neutral, in contrast to the usual electropositive features found in other 4-OT family members, suggesting that AfDmpI might accommodate hydrophobic substrates. A kinetic analysis has been carried out, but does not provide any clues about the type of reaction the enzyme might catalyze.
tautomerase 超家族由结构同源的蛋白组成，这些蛋白的特征是具有 β-α-β 折叠和催化氨基末端脯氨酸。4-氧代戊烯酸 tautomerase (4-OT) 家族成员已被鉴定，并根据多个序列比对和关键催化及结构残基的保守性分为五个亚家族。两个亚家族的代表性成员已经被克隆、表达、纯化，并进行了动力学和结构特征分析。来自幽门螺旋杆菌 (HpDmpI) 的 DmpI 的晶体结构（属于 3 亚家族的 4-OT 同源物）已在两种不同的空间群中被确定到高分辨率（1.8Å 和 2.1Å）。HpDmpI 是一个同六聚体，其活性位点腔包括 Pro-1，但缺乏在 4-OT 中发现的 Arg-11 和 Arg-39。相反，侧链 Lys-36 以类似于在三聚体巨噬细胞移动抑制因子 (MIF) 中观察到的方式取代 Arg-11，MIF 是超家族中另一个家族的标题蛋白。活性位点的静电表面也非常不同，表明 HpDmpI 可能更喜欢小的、单酸底物。对该酶的动力学分析与结构分析一致，但该酶的生物学作用仍不清楚。来自产甲烷球菌 (AfDmpI) 的 DmpI 的晶体结构（属于 4-OT 亚家族-4 的同源物）已被确定到 2.4Å 分辨率。AfDmpI 也是一个同六聚体，具有一个推测的活性位点腔，包括 Pro-1，但缺乏任何其他容易被识别为与 4-OT 活性相关的催化残基。事实上，活性位点的静电势有很大的不同，因为它主要是中性的，与其他 4-OT 家族成员中常见的正电性特征形成对比，这表明 AfDmpI 可能容纳疏水性底物。已经进行了动力学分析，但没有提供任何关于该酶可能催化的反应类型的线索。
